The present invention relates generally to the connections that integrate some components of a nuclear reactor pressure vessel; and more particularly to an apparatus and system for mitigating the gaps between an inlet mixer and corresponding adjust screws.
A Boiling Water Reactor (BWR) is designed to generate steam in a reactor pressure vessel (RPV) by heating the water surrounding uranium-containing tubes of fuel assemblies located in the RPV core regions. The RPV has recirculation loops designed to facilitate the circulation of water in the core regions. The recirculation loops generally include large centrifugal pumps that pump water out of the RPV and return the water to the inlets of jet pump assemblies located in annular regions in the RPV surrounding the core regions. The jet pump assemblies are designed to entrain the surrounding water in the annular regions and then discharge the water in a manner that induces a desired flow pattern in the core region.
The jet pump assemblies are subject to vibrations caused by hydraulic forces due to the flow of water and/or by the rotation of the centrifugal pumps. Thus, in one BWR design, the jet pump assemblies are horizontally supported against vibration with a jet pump restrainer assembly including a bracket using a three-point suspension system. A multi-point system generally includes a wedge movably mounted on a vertically oriented guide rod that is attached to a jet pump assembly and extends through the space between the bracket and the jet pump. The wedge is designed to slide downwardly under the force of gravity into the space between the bracket and the jet pump assembly, urging the jet pump against the adjustment screws.
Traditionally, gaps develop between adjustment screws and the inlet mixer. This gap is commonly filled with an auxiliary wedge. The auxiliary wedge inhabits the gap and serves to reestablish a desired multi-point contact in the bracket. Commonly, this multi-point contact involves two adjustment screws and the main wedge.
There are a few issues with using an auxiliary wedge. Installation typically requires the following: multiple field measurements; multiple independent calculations of final machining dimensions; machining; and inspection of the machined parts. These processes can add several man-hours to an outage. In addition, an auxiliary wedge may not limit the movement of the mixer pipe away from the adjustment screws.
For the foregoing reasons, an operator of a RPV may desire an apparatus for addressing mitigating adjustment screw gaps. The apparatus should limit the movement of the mixer pipe away from the adjustment screws.